Experimental and analytical studies on contact irreversible electroporation for superficial tumor treatment

Irreversible electroporation (IRE) is attracting much attention as a less-invasive therapy to ablate abnormal tissues. With a pair of electrodes inserted into the tissue, the IRE perforates the targeted cells non-thermally by a train of intensive electric pulses that exceeds a certain threshold. Since only the cells are necrotized percutaneously, the extracellular matrix is kept intact in the IRE, which is favorable for prompt tissue regeneration. In this study, we demonstrated that the IRE is also applicable to treat superficial targets such as melanoma, nevus, and tumors on gastrointestinal surface. A pair of 1-mm dia. stainless steel rods fixed 5 mm apart in an acrylic plate was contacted on an agarose gel containing fibroblasts. A sequence of 15 to 90 pulses of 1 kV was then applied to the gel via electrodes. All pulses were 10 μs in length and oscillated at 100 ms intervals. The boundary between dead and alive cell regions was determined at the surface and vertical cross section by using fluorescent staining. The necrotic cell area was also predicted by a numerical solution to the equation of electric field. Those determined with an assumption that the potential difference of 1 V between the cell membrane induces irreversible cell breakdown agreed well with the necrotic cell area and maximal depth in the experiment at low pulse number. However, the experiment showed the increase in the necrotic area with increasing the pulse repetition. Since application of multiple pulses perforates the highly resistive cell membrane, our study indicated the importance of taking into account the change in the electrical properties due to cell destruction.